I am not denying that there is entirely new storyline material, quests, and locations but it is nothing I could not accomplish with the help of 3 or 4 friends. If I would have started when F3 were first released, I promise you I could have written an expansion/mod of the same caliber and depth as Fallout: New Vegas.
Just saying.
No you couldn't, and anyone who has ever worked on even a large mod project is laughing at you right now. I don't mean that to be offensive, but you're statement is so idiotic as to be funny.Ive seen very motivated mod teams of 10-15 people take years to make something that is half the quality of New Vegas. I've even worked on large mod teams (For OFP and ArmA games, Not for Fallout 3) that, while motivated, would never have come close to replicating the difference between New Vegas and Fallout 3.
The reason why is simple: There is a lot more to New Vegas then just a new map, quest, and storyline. First of all, there are quite a few changes to the core game engine, which you could not have done in a mod since you would lack access to the source code. Then what about all that new dialogue? Not only would you're team have to write it all... you would also have to add it to the game, test it all, and record it. That alone could take 2-4 PAID FULL TIME EMPLOYEES months and months of work (this alone is beyond the scope of a small mod team btw). What about all the new art assets? Making high quality game models is not a quick process just so you know.
Then what about the stuff you casually gloss over like its quick and easy... like making an entire new map. Making the Fallout New Vegas map would take a small team forever. Sure, some hack job could throw together a map that's the same size in a couple months that has a bunch of towns and such thrown all over randomly... but it would lack the detail of a polished professional map and clearly be a hack job that no one would play. Mapping actually takes a while. Good mappers might spend hours working on one very small area... especially when you get into the small detailing bits, like placing every single in game item with a purpose. Could a mod team make a FO3/NV quality map in two years? Sure they could... but then you actually have to populated it with well designed and planned out quests and NPCs. Again, as most things, its not just a "Well this guy looks good here" and "I'll just throw together a quest and put it here" situation. It takes time to write out, plan, and then implement hundreds of quests and thousands of NPCs. Oh, and perhaps you're biggest obstacle which I have touched on twice would be what kills more mods then anything else... its hard to find people who will devote all of their free time over the span of many months to work on a project for which they are not paid, and will never see a dime (not to mention listening to "Whens it ready?" every 5 minutes).
I didn't even cover some important things, like sound and particle effects which again, could take a couple PAID GAME DEVELOPERS months of work... but you get the picture. You think you can do all of that, and do it on a professional level, with a 4 man mod team working in their spare time over a two year period? If so perhaps you should actually try modding/game development... its far more time consuming then you might think. There is no way in hell an un-paid 4 man mod team could come anywhere close to making a New Vegas level mod for Fallout 3 inside of two years. If you doubt me, try it... you will give up in a week once you see just how much you would be biting off.
That all has nothing to do with the fact I happen to like Fallout 3 and New Vegas... I don't svck up to games I enjoy. It has everything to do with the fact I have been a modder, and amateur game maker for years and know a little something about the subject.
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On the original subject: Yes, New Vegas feels a bit like an expansion... but that's because they share the same engine. One can even argue that Fallout 3 was just a mod of Oblivion. But you know what, there are many "new" games out there that cost $50-60 that I get a whopping 4-5 hours of gameplay out of. New Vegas is going to give me between 20-40 hours of fun, and likely a lot more with mods... expansion or not, thats more then worth $50 for me.